1. Field of Art
The disclosure generally relates to the field of analog-to-digital converters (ADCs), and more specifically to calibrating pipeline ADCs.
2. Description of the Related Art
An analog-to-digital converter (ADC) is an electronic device that converts an analog signal (e.g., voltage signal) into a series of discrete digital values. The digital values are proportional to the magnitude of the analog signal. One type of ADC is a pipeline ADC which includes multiple stages in series. The first stage performs a quantization and outputs the resulting bits. Additionally, the first stage amplifies a residue voltage, which is the error that remains after the first stage performs the quantization. The amplified residue is output to the second stage of the pipeline ADC for further quantization. The second stage also outputs bits and generates another residue voltage that is fed to the third stage for quantization. The process continues until all the bits of the ADC have been resolved.
In order for a stage in the pipeline ADC to generate the appropriate residue voltage, the stage needs an amplifier with a certain gain. Any deviation from that gain value causes non-linearities in the transfer function of the ADC. In typical switched-capacitor implementations of a stage, deviation from the ideal gain value is caused by capacitor mismatches and finite low frequency gain of the amplifier (usually referred to as the “DC gain”). To achieve high resolution with low power dissipation, digital calibration may be used to correct the deviations. To accurately correct the deviations, it is necessary to determine calibration coefficients for the stages.